The present invention pertains to an apparatus for and a method of uniformly projecting a high level of radiation onto elongated three-dimensional objects so as to uniformly treat the surfaces of the objects. More particularly, the present invention pertains to an apparatus and a method providing substantially two-dimensionally uniform irradiation of elongated three-dimensional objects while the objects are rotating and moving across the irradiator, with a high level of irradiance and with a constant radiation dose on the surfaces of the objects during each phase of the rotation and movement.
Various manufacturing processes include treating an object having an elongated three-dimensional surface, such as a curved surface, by irradiating the surface with, for example, ultraviolet (UV) light or other radiation. The radiation treatment may be related to curing, surface modification, disinfection, advanced oxidation or some other procedure. By way of example, in some printing processes a printed pattern is cured by irradiating the pattern. Obtaining a high quality, uniform product requires irradiating a two-dimensionally uniform high level of radiation over the entire object area of interest. Otherwise irregularities in the finished product may result.
Existing devices often expose the central area of an irradiated surface to more radiation than the edge areas of the surface. The areas of high radiation may receive more than the desired level, possibly causing damage, while the areas of low radiation may be undertreated.
Various techniques have been used in the past to control the uniformity of irradiation of planar target surfaces. By way of example, U.S. Pat. No. 4,010,374 discloses an UV light processor including a primary light source which exposes a target surface on a work piece to UV light, with the UV flux incident per unit area of the target surface greater in the central region of the surface than at edges of the surface, and a secondary light source, which is located in a different plane than the primary light source and which exposes the target surface to UV light, with the UV flux incident per unit area of the surface greater at the edge areas of the target surface than at the central region. Not only is such an UV light processor complex and expensive to manufacture and to operate, but also it is difficult to control in a manner that maintains the UV radiation received at the edge areas of the target surface from the secondary source at substantially the same level as the UV radiation received at the central area of the target surface from the primary source.
U.S. Pat. No. 4,276,479 discloses a tunnel type irradiation chamber through which an object to be treated is conveyed. A plurality of cylindrical UV-lenses are within the tunnel type chamber. Two sets of radiation sources, providing light of two different wavelengths, are within the chamber, providing irradiation in two stages. This apparatus is also complex to control, but yet it may not provide uniform radiation distribution on the object surface.
U.S. Pat. No. 4,348,015 shows a radiation projection system including complex lenses in order to provide uniform irradiance. Numerous other systems have been attempted. These generally are complex and expensive, both to construct and to operate. Even so, they generally have difficulty in achieving uniform irradiance, especially two-dimensionally uniform irradiance of elongated curved objects.
The present invention is an apparatus and a method providing substantially two-dimensionally uniform irradiation of elongated three-dimensional objects with a high level of radiation. While the present invention is described hereinbelow with reference to irradiation of curved objects, it is to be understood that it is equally applicable to other three-dimensional objects. In accordance with the present invention at least one source is provided for producing radiation to irradiate an elongated curved object surface. Each source may include an elongated discharge bulb. Each radiation source is arranged within a corresponding elongated elliptical reflecting trough, with the radiation source spaced from the focal axis within the trough. Preferably, planar reflectors extend from the troughs to the target surface. Preferably, also, these reflectors are pivotally attached to the troughs so as to accommodate various sizes of target surfaces and to aid in optimization of the uniformity of the radiation distribution. Additionally, preferably each radiation source is on the major axis of the ellipse defining its trough and is spaced from the focal axis within the trough. Further, preferably, the position of each reflecting trough is adjustable in the direction of the minor axis of the ellipse defining the trough. Each source of radiation can be a light source, preferably a source of ultraviolet light such as a microwave electrodeless discharge bulb, an arc discharge bulb, or a fluorescent discharge bulb. The objects are moved past the radiation source and are rotated at a linear speed and an angular velocity determined by the desired dose of radiation.